Process for mild hydrocracking of petroleum cuts using a catalyst containing at least two dealuminated Y zeolites

ABSTRACT

A mild hydroconversion process for petroleum cuts using a catalyst comprising at least one matrix, at least one Y zeolite with a lattice parameter which is in the range 24.15 Å to 24.38 Å (1 nm--10 Å), at least one Y zeolite with a lattice parameter of more than 24.38 Å and less than or equal to 24.51 Å, and at least one hydro-dehydrogenating element.

BACKGROUND OF THE INVENTION

The present invention concerns a process for mild hydroconversion ofpetroleum cuts using a catalyst comprising at least two dealuminated Yzeolites associated with a matrix which is normally amorphous or of lowcrystallinity.

Mild hydrocracking of heavy petroleum cuts is a refining process whichproduces, from surplus and heavy feeds of low upgradability, lighterfractions such as gasolines, aviation fuel and light gas oils which therefiner needs in order to adapt his production to demand. In comparisonwith catalytic cracking, catalytic hydrocracking is important for theproduction of improved quality middle distillates, aviation fuels andgas oils. In contrast, the gasoline produced has a much lower octanenumber than that from catalytic cracking.

The catalysts used in mild hydrocracking are all bifunctional,associating an acid function with a hydrogenating function. The acidfunction is provided by supports with large surface areas of fairly lowsuperficial acidity, such as halogenated aluminas (in particularchlorinated or fluorinated aluminas), combinations of boron oxides andaluminium oxides, and amorphous silica-aluminas. The acidity is usuallyfar lower than that of zeolites. The hydrogenating function is providedeither by one or more metals from group VIII of the periodic table, suchas iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridiumand platinum, or by the association of at least one metal from group VIof the periodic table, such as chromium, molybdenum and tungsten, and atleast one group VIII metal, preferably a non-noble metal.

The great majority of conventional mild hydrocracking catalysts containweakly acidic supports, such as amorphous silica-aluminas. Amorphoussilica-aluminas form a family of low acidity supports.

Many commercial mild hydrocracking catalysts contain silica-aluminaassociated with either a group VIII metal or, as is preferable when thequantity of heteroatomic poisons in the feed to be treated exceeds 0.5%by weight, with an association of sulphides of metals from groups VIBand VIII. Such systems have very good selectivity for middle distillatesand the products formed are of quite good quality. The disadvantage ofall of those catalytic systems based on an amorphous support is, as hasalready been stated, their low activity.

The present invention overcomes these disadvantages. It provides a mildhydroconversion process using a catalyst comprising at least one matrix,at least one Y zeolite, Y1, with a lattice parameter which is in therange 24.15 Å to 24.38 Å (1 nm=10 Å), at least one Y zeolite, Y2, with alattice parameter of more than 24.38 Å and less than or equal to 24.51Å, and at least one hydro-dehydrogenating element.

In the remainder of the text, the lattice parameter units will beexpressed in Å (1 nm=10 Å).

The catalyst and support of the present invention thus comprises atleast two Y zeolites with faujasite structure ("Zeolite MolecularSieves: Structure, Chemistry and Uses", D. W. Breck, J. Wiley & Sons,1973) which can either be in the hydrogen form or in a form which ispartially exchanged with metal cations, for example with alkaline-earthmetal cations and/or cations of rare earth metals with atomic number 57to 71 inclusive. The first, known here as Y1, has a lattice parameter ofmore than 24.15 Å up to 24.38 Å. The second, known here as Y2, has alattice parameter of more than 24.38 Å and less than or equal to 24.51Å. The Y1/Y2 weight ratio, i.e., the ratio between the first and thesecond zeolite, is in the range 0.1 to 100, advantageously in the range0.1 and 80, more advantageously in the range 0.1 to 50, preferably inthe range 0.3 to 30, and more preferably in the range 0.5 to 10. Thetotal weight content of the matrix with respect to the support (thesupport is constituted by the matrix and the totality of the Y zeolites)is in the range 20% to 99%, preferably in the range 25% to 98%, morepreferably in the range 40% to 97% and advantageously in the range 65%to 95%.

The preferred acid zeolite Y1 is characterized by variousspecifications: a lattice parameter in the range 24.15 Å to 24.38 Å; aframework SiO₂ /Al₂ O₃ molar ratio, calculated using theFichtner-Schmittler correlation (in Cryst. Res. Tech. 1984, 19, K1) inthe range about 500 to 21; a sodium content of less than 0.15% by weightdetermined on zeolite calcined at 1100° C.; a sodium ion take-upcapacity C_(Na), expressed in grams of Na per 100 grams of modified,neutralised then calcined zeolite, of more than about 0.85; a specificsurface area, determined using the BET method, of more than about 400 m²/g, preferably more than 550 m² /g; a water vapour adsorption capacityat 25° C. for a partial pressure of 2.6 torrs (i.e., 34.6 MPa) of morethan about 6%, and a pore distribution wherein between 1% and 20%,preferably between 3% and 15%, of the pore volume is contained in poreswith a diameter between 20 Å and 80 Å, the major part of the remainderof the pore volume being contained in pores with a diameter of less than20 Å.

The other preferred acid zeolite Y2 is characterized by variousspecifications: a lattice parameter in the range 24.38 Å to 24.51 Å; aframework SiO₂ /Al₂ O₃ molar ratio, calculated using theFichtner-Schmittler correlation (in Cryst. Res. Tech. 1984, 19, K1) ofless than about 21 and greater than or equal to 10; a sodium content ofless than 0.15% by weight determined on zeolite calcined at 1100° C.; asodium ion take-up capacity C_(Na), expressed in grams of Na per 100grams of modified, neutralized then calcined zeolite, of more than about0.85; a specific surface area, determined using the BET method, of morethan about 400 m² /g, preferably more than 550 m² /g; a water vaporadsorption capacity at 25° C. for a partial pressure of 2.6 torrs (i.e.,34.6 MPa) of more than about 6%, and a pore distribution wherein between1% and 20%, preferably between 3% and 15%, of the pore volume iscontained in pores with a diameter between 20 Å and 80 Å, the major partof the remainder of the pore volume being contained in pores with adiameter of less than 20 Å.

The catalyst and support thus comprise at least these two zeolites Y1and Y2 but it can contain more than two provided that these zeoliteshave the lattice parameters of Y1 or Y2.

Any method which can produce zeolites Y1 and Y2 having thecharacteristics defined above is suitable.

The catalyst of the present invention also comprises at least one matrixwhich is normally amorphous or of low crystallinity selected, forexample, from the group formed by alumina, silica, magnesia, titaniumoxide, zirconia, aluminium, titanium or zirconium phosphates, clay,boron oxide and combinations of at least two of these compounds.

The matrix is preferably selected from the group formed by silica,alumina, magnesia, silica-alumina combinations, and silica-magnesiacombinations.

The catalyst of the present invention can be prepared using any of themethods known to the skilled person. It is advantageously obtained bymixing the matrix and zeolites then forming. The hydrogenating elementis introduced during mixing, or it can be introduced after forming(preferred). Forming is followed by calcining, the hydrogenating elementbeing introduced before or after calcining. In all cases, thepreparation is finished by calcining at a temperature of 250° C. to 600°C. One preferred method consists of mixing Y zeolites of faujasitestructural type in a wet alumina gel for several tens of minutes, thenpassing the paste obtained through a die to form extrudates with apreferred diameter of between 0.4 mm and 4 mm.

The catalyst also includes a hydrogenating function. Thehydro-dehydrogenating function is provided by at least one group VIIImetal or a compound of a group VIII metal, in particular nickel andcobalt. A combination of at least one metal or compound of a metal fromgroup VI of the periodic table (in particular molybdenum or tungsten)and at least one metal or compound of a metal from group VIII in theperiodic table, preferably a non noble metal (in particular cobalt ornickel), can be used. The hydrogenating function itself as defined abovecan be introduced into the catalyst at various stages of the preparationand in various ways.

It can be introduced only in part (for example for associations ofoxides of group VI and group VIII metals) or in total when mixing thetwo zeolite types with the gel of the oxide selected as the matrix, theremainder of the hydrogenating element(s) then being introduced aftermixing, and more generally after calcining. The group VIII metal ispreferably introduced simultaneously with or after the group VI metal,whatever the method of introduction. It can be introduced in one or moreion exchange operations on the calcined support constituted by zeolitesdispersed in the selected matrix, using solutions containing precursorsalts of the selected metals when these are from group VIII. It can beintroduced using one or more operations to impregnate the formed andcalcined support with a solution of precursors of oxides of group VIIImetals (in particular cobalt and nickel) when the precursors of oxidesof metals from group VI (in particular molybdenum or tungsten) have beenintroduced on mixing the support. Finally, it can be introduced by oneor more operations to impregnate the calcined support, constituted byzeolites and the matrix, with solutions containing precursors of oxidesof group VI and/or group VIII metals, the precursors of oxides of groupVIII metals preferably being introduced after those of group VI or atthe same time as the latter.

When the elements are introduced by impregnating several times with thecorresponding precursor salts, intermediate calcining of the catalystmust be carried out at a temperature which is in the range 250° C. to600° C.

The total concentration of oxides of group VIII and VI metals is in therange 1% to 40% by weight of the catalyst obtained after calcining,preferably in the range 3% to 30% and advantageously in the range 8% to40%, more advantageously 10% to 40% and even more advantageously, 10% to30%. The ratio of group VI metal(s) to group VIII metal(s) is generallyin the range 20 to 1.25, preferably in the range 10 to 2, expressed byweight as the metal oxides. The catalyst can also contain phosphorous.The concentration of phosphorous oxide (P₂ O₅) is generally in the range0.1% to 15%, preferably in the range 0.15% to 10% by weight.

Impregnation of molybdenum can be facilitated by adding phosphoric acidto the molybdenum salt solutions.

The catalysts obtained, in the form of oxides, can optionally be atleast partially changed into the metallic or sulphide form.

They are charged into the reactor and used for mild hydrocracking, inparticular of heavy cuts. Their activity is improved compared with theprior art.

The petroleum cuts to be treated have boiling points of more than 100°C. Examples are kerosines, gas oils, vacuum distillates, deasphalted orhydrotreated residues, or equivalents thereof. The feeds, which arehighly charged with N and S, are preferably hydrotreated first. Theheavy cuts are preferably constituted by at least 80% by volume ofcompounds with boiling points of at least 350° C., preferably between350° C. and 580° C. (i.e., corresponding to compounds containing atleast 15 to 20 carbon atoms). They generally contain heteroatoms such assulphur and nitrogen. The nitrogen content is usually in the range 1 to5000 ppm by weight and the sulphur content is in the range 0.01% to 5%by weight. Hydrocracking conditions, such as temperature, pressure,hydrogen recycle ratio, and hourly space velocity, can vary depending onthe nature of the feed, the quality of the desired products, and thefacilities available to the refiner.

When hydrotreatment is necessary, the petroleum cut conversion processis carried out in two steps, the catalysts of the invention being usedin the second step.

Catalyst 1 of the first hydrotreatment step comprises a matrix,preferably based on alumina, and preferably containing no zeolite, andat least one metal with a hydro-dehydrogenating function. This matrixcan also be constituted by, or include, silica, silica-alumina, boronoxide, magnesia, zirconia, titanium oxide or a combination of theseoxides. The hydro-dehydrogenating function is provided by at least onemetal or compound of a metal from group VIII of the periodic table suchas nickel or cobalt. A combination of at least one metal or compound ofa metal from group VI of the periodic table (in particular molybdenum ortungsten) and at least one metal or compound of a metal from group VIII(in particular cobalt or nickel) from the periodic table can be used.The total concentration of oxides of group VI and group VIII metals isin the range 5% to 40% by weight, preferably in the range 7% to 30% byweight, and the ratio of group VI metal(s) to group VIII metal(s) is inthe range 1.25 to 20, preferably in the range 2 to 10, expressed byweight as the metal oxides. The catalyst can also contain phosphorous.The phosphorous content, expressed as the concentration of diphosphorouspentoxide P₂ O₅, is generally at most 15%, preferably in the range 0.1%to 15%, and more preferably in the range 0.15% to 10% by weight.

The first step is generally carried out at a temperature of 350° C. to460° C., preferably 360° C. to 450° C., at a total pressure of 2 MPa toless than 8 MPa, preferably 2 MPa to 7 MPa, an hourly space velocity of0.1 to 5 h⁻¹, preferably 0.2 to 2 h⁻¹, and with a quantity of hydrogenof at least 100Nl/Nl of feed, preferably 260-2000 Nl/Nl of feed.

In the case of the conversion step using the catalyst of the invention(second step), the temperatures are generally 230° C. or more, usuallyin the range 350° C. to 470° C., preferably in the range 350° C. to 460°C. The pressure is 2 MPa or more, generally more than 2.5 MPa. Thepressure is less than 8 MPa and generally less than or equal to 7 MPa.The quantity of hydrogen is a minimum of 1001/1 of feed, usually in therange 150 to 1500 l/l of hydrogen per litre of feed. The hourly spacevelocity is generally in the range 0.15 to 10 h⁻¹.

The parameters which are important to the refiner are the activity andselectivity towards middle distillates. Fixed targets must be achievedunder conditions which are compatible with economic reality. Underconventional hydrocracking conditions, this type of catalyst can produceselectivities of more than 65%, and generally more than 75%, with levelsof conversion of more than 25% or 30% and generally less than 60%.Finally, because of the composition of the catalyst, it can readily beregenerated.

Surprisingly, we have been able to establish that, in accordance withthe invention, a catalyst containing at least two dealuminated Yzeolites can produce a selectivity for middle distillates which issubstantially improved compared with prior art catalysts. The followingexamples illustrate the present invention without in any way limitingits scope.

EXAMPLES Example 1

Production of Catalyst C1

Catalyst C1 was produced as follows: 20% by weight of a Y zeolite with alattice parameter of 24.42 Å was used, mixed with 80% by weight of SB3type alumina from Condea. The mixed paste was then extruded through a1.4 mm diameter die. The extrudates were dried overnight at 120° C. inair then calcined at 550° C. in air. The extrudates were dry impregnatedusing a solution of a mixture of ammonium heptamolybdate, nickel nitrateand orthophosphoric acid, dried overnight at 120° C. in air thencalcined in air at 550° C. The concentrations of active oxides were asfollows (with respect to the catalyst):

2.6% by weight of nickel oxide NiO;

12.7% by weight of molybdenum oxide MoO₃ ;

5.5% by weight of phosphorous oxide P₂ O₅.

Example 2

Production of Catalyst C2.

Catalyst C2 was produced as follows: 20% by weight of a Y zeolite with alattice parameter of 24.28 Å was used, mixed with 80% by weight of SB3type alumina from Condea. The mixed paste was then extruded through a1.4 mm diameter die. The extrudates were dried overnight at 120° C. inair then calcined at 550° C. in air. The extrudates were dry impregnatedusing a solution of a mixture of ammonium heptamolybdate, nickel nitrateand orthophosphoric acid, dried overnight at 120° C. in air thencalcined in air at 550° C. The concentrations of active oxides were asfollows (with respect to the catalyst):

2.7% by weight of nickel oxide NiO;

12.8% by weight of molybdenum oxide MoO₃ ;

5.4% by weight of phosphorous oxide P₂ O₅.

Example 3

Production of Catalyst C3

Catalyst C3 was produced as follows: 10% by weight of a Y zeolite with alattice parameter of 24.42 Å and 10% by weight of a Y zeolite with alattice parameter of 24.28 Å were used, mixed with 80% by weight of SB3type alumina from Condea. The mixed paste was then extruded through a1.4 mm diameter die. The extrudates were dried overnight at 120° C. inair then calcined at 550° C. in air. The extrudates were dry impregnatedusing a solution of a mixture of ammonium heptamolybdate, nickel nitrateand orthophosphoric acid, dried overnight at 120° C. in air thencalcined in air at 550° C. The concentrations of active oxides were asfollows (with respect to the catalyst):

2.6% by weight of nickel oxide NiO;

12.7% by weight of molybdenum oxide MoO₃ ;

5.4% by weight of phosphorous oxide P₂ O₅.

Example 4

Comparison of C1, C2 and C3

The catalysts prepared as in the preceding examples were used under mildhydrocracking conditions on a petroleum feed with the followingprincipal characteristics:

    ______________________________________    Initial point          277° C.    10% point              381° C.    50% point              482° C.    90% point              531° C.    End point              545° C.    Pour point             +39° C.    Density (20/4)         0.919    Sulphur (% by weight)  2.46    Nitrogen (ppm by weight)                           930    ______________________________________

The catalytic test unit comprised two fixed bed reactors operating inupflow mode. 40 ml of catalyst was introduced into each catalyst. Afirst hydrotreatment step catalyst 1, HR360 sold by Procatalyse,comprising a group VI element and a group VIII element deposited onalumina, was introduced into the first reactor, into which the feed wasinitially fed. A second step catalyst 2, i.e., the hydroconversioncatalyst, was introduced into the second reactor, into which the feedwas finally fed. The two catalysts underwent in-situ sulphurisationbefore the reaction. It should be noted that any in-situ or ex-situsulphurisation method would have been suitable. Once sulphurisation hadbeen carried out, the feed described above could be transformed. Thetotal pressure was 5 MPa, the hydrogen flow rate was 500 litres ofgaseous hydrogen per litre of feed injected, and the hourly spacevelocity was 0.5 h⁻¹.

The catalytic performances were expressed as the gross conversion at400° C. and as the gross selectivity. These catalytic performances weremeasured on the catalyst after a period of stabilisation had passed,generally at least 48 hours.

The gross conversion, GC, is defined as: ##EQU1##

The gross selectivity, GS, is defined as: ##EQU2##

The following table shows the gross conversion at 400° C. and the grossselectivity for the three catalysts.

    ______________________________________              GC (% by weight)                         GS    ______________________________________    C1          55.5         77.3    C2          45.3         82.5    C3          49.6         82.4    ______________________________________

Using a mixture of zeolites produced a high level of conversion and veryhigh selectivity, substantially higher than that of catalyst C1 and thesame as that of catalyst C2, while the level of conversion was high: again of 4.3% by weight over catalyst C2 was observed.

We claim:
 1. A process for the conversion of a petroleum cut comprisingcontacting the cut with a catalyst comprising at least one matrix, atleast one Y zeolite (Y1) with a lattice parameter of 24.15 Å to 24.38 Å,at least one Y zeolite (Y2) with a lattice parameter of more than 24.38Å and less than or equal to 24.51 Å, and at least onehydro-dehydrogenating element, in the presence of a quantity ofhydrogen.
 2. A process according to claim 1, in which the cut has firstundergone hydrotreatment.
 3. A process according to claim 2, in whichthe hydrotreatment catalyst comprises a matrix which is alumina, silica,boron oxide, magnesia, zirconia, titanium oxide or a combinationthereof, and at least one metal having a hydro-dehydrogenating function,which is a group VI or group VIII metal, the total concentration ofoxides of said metal being 5% to 40% by weight, the weight ratio ofgroup VI metal oxides to group VIII metal oxides being 1.25 to 20, andthe catalyst optionally containing at most 15% by weight ofdiphosphorous pentoxide.
 4. A process according to claim 2, in whichhydrotreatment takes place at a temperature of between 350-460° C., at apressure of at least 2 MPa to less than 8 MPa, with a quantity ofhydrogen of at least 100 Nl/l of feed and an hourly space velocity of0.1-5 h⁻¹.
 5. A process according to claim 1, in which the cut containsat least 80% by volume of compounds with boiling points of at least 350°C.
 6. A process according to claim 1, in which the petroleum cut is agas oil, a vacuum distillate, a deasphalted residue or a hydrotreatedresidue.
 7. A process according to claim 1, in which the conversioncatalyst comprises a matrix which is alumina, silica, magnesia, titaniumoxide, zirconium oxide an aluminium phosphate, a titanium phosphate, azirconium phosphate, boron oxide, clay or a mixture thereof.
 8. Aprocess according to claim 1, in which the hydro-dehydrogenating elementis an element from group VIII or an element from group VI of theperiodic table.
 9. A process according to claim 1, in which the contentof the matrix in the catalyst support is 20% to 98% by weight.
 10. Aprocess according to claim 1, in which the Y1/Y2 weight ratio is 0.1 to100.
 11. A process according to claim 1, in which the Y1/Y2 weight ratiois 0.3 to
 30. 12. A process according to claim 1, in which the catalystcontains 1% to 40% by weight of oxides in the totality of thehydrogenating elements.
 13. A process according to claim 1, in which thecatalyst further contains 0.1% to 15% by weight of diphosphorouspentoxide.
 14. A process according to claim 1, in which the catalyst isprepared by mixing the zeolites with the matrix, introducing at least aportion of the hydro-dehydrogenating elements, forming then calcining.15. A process according to claim 1, in which the catalyst is prepared bymixing the zeolites and the matrix, forming, calcining then introducingthe hydro-dehydrogenating element(s).
 16. A process according to claim1, in which the catalyst is prepared by mixing the zeolites with thematrix, forming, introducing the hydro-dehydrogenating element(s), thencalcining.
 17. A process according to claim 14, in which thehydro-dehydrogenating group VIII element(s) is/are introduced after orsimultaneously with the introduction of the hydro-dehydrogenating groupVI element(s).
 18. A process according to claim 1 with a sulphurizedcatalyst.
 19. A process according to claim 1, conducted at a temperatureof at least 230° C., a pressure of at least 2 MPa and less than 8 MPa, aquantity of hydrogen of at least 100 Nl/l of feed and an hourly spacevelocity of 0.15 to 10h⁻¹.
 20. A process according to claim 1, furthercomprising mixing the zeolites and the matrix, forming, calcining thenintroducing the hydro-dehydrogenating elements(s), prior to contactingwith the cut.
 21. A process according to claim 1, further comprisingmixing the zeolites and the matrix, forming, introducing thehydro-dehydrogenating elements(s), then calcining, prior to contactingwith the cut.
 22. A process according to claim 1, wherein (Y1) has alattice parameter of 24.28 to 24.38 and (Y2) has a lattice parameter of24.42 to 24.51.
 23. A process according to claim 1, wherein (Y1) has alattice parameter of 24.15 to 24.28 and (Y2) has a lattice parameter of24.42 to 24.51.
 24. A process according to claim 1, wherein (Y1) has alattice parameter of 24.28 and (Y2) has a lattice parameter of 24.42.